SPC AC 071300

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0700 AM CST Tue Feb 07 2017

   Valid 071300Z - 081200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF LA/MS/AL TO FL PANHANDLE...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE GULF
   COAST STATES/LOWER MS RIVER VALLEY AND TN VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
   GULF COAST TO THE OHIO VALLEY AND MIDWEST...

   ...SUMMARY...
   Severe thunderstorms are expected today especially across the lower
   Mississippi Valley and central Gulf Coast states, but some strong to
   severe thunderstorms may occur as far north as the Tennessee Valley
   and Ohio Valley.

   ...Portions of LA/MS/AL to FL Panhandle...
   A southern-stream shortwave trough (and related mid/high-level speed
   max) will continue to amplify and spread generally
   east-southeastward today toward the central Gulf Coast States.
   Strengthening low/mid-level southwesterly winds will support the
   continued northeastward transport of low/middle 60s F surface
   dewpoints across additional portions of MS/AL. 

   Showers/thunderstorms are already increasing within the modestly
   moist early-day warm sector across southern/eastern LA into MS. Many
   of these storms should become increasingly surface based into late
   morning/early afternoon as additional moistening and destabilization
   occurs. 12Z observed soundings from Shreveport (SHV) and Lake
   Charles (LCH) sample severe-favorable thermodynamic profiles with
   very steep mid-level lapse near or excess of 8.0 C/km, aside from
   35-45 kt of effective shear.

   Steadily increasing deep-tropospheric winds and lengthening
   hodographs, in conjunction with cool mid-level temperatures (roughly
   -14C to -17C at 500 mb) and steepening lapse rates, appears likely
   to support supercells capable of large hail, along with some
   tornado/damaging wind risk, especially from mid/late morning into
   the afternoon. Storms may merge over time and grow upscale with at
   least a modestly increased damaging wind risk into AL and the FL
   Panhandle this afternoon, although the eastward progression of the
   presumed convective line may eventually outrun the greater low-level
   moistening/destabilization. 

   For additional details on the expected early-day evolution of
   storms, please reference Mesoscale Discussion 144.

   ...Tennessee Valley/Ohio Valley/Midwest...
   Ahead of a cold front, moist advection will continue to occur in
   concert with 50+ knot low-level southwesterly winds. Mostly linear
   bands of strong to locally severe convection are ongoing early this
   morning from east-central AR into western TN. These storms should
   develop eastward across additional portions of TN and northern
   portions of MS/AL. While these storms are likely to develop east of
   the primary moist/instability axis, a modestly increasing potential
   for damaging winds, some hail and brief tornado risk can be expected
   during the day eastward into at least middle TN and northern
   portions of MS/AL. 

   Farther north into the Ohio Valley and Midwest, current thinking is
   that extensive ongoing precipitation south of the Ohio River and
   related cloud cover will tend to hinder appreciable destabilization.
   While weak buoyancy/strong vertical shear could support some
   stronger/potentially severe low-topped storms, the overall severe
   risk should remain limited.

   ..Guyer.. 02/07/2017

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